1. Field of the Invention
The present invention relates to a humidifier for humidifying a gas to be supplied to an apparatus such as a fuel cell, and particularly to a humidifier including hollow fiber membranes having a water permeability in walls thereof.
2. Description of the Related Art
Fuel cells such as Polymer Electrolyte Fuel Cells (PEFC) require a humidifier for humidifying a fuel gas such as hydrogen and oxidant gas such as oxide.
JP2004-6099A discloses, in FIG. 11 thereof, a humidifier including hollow fiber membranes having a water permeability in wall thereof housed in a case for humidifying air through exchanging water by the hollow fiber membranes between an much moist off-gas (having much water) exhausted from a fuel cell and air (oxidant gas) supplied to the fuel cell.
However, in the humidifier disclosed in JP2004-6099A, the hollow fiber membranes may stick to an inner circumferential surface of the case, closing gas outlets due to a flow of the gas, while the gas flows outside the hollow fiber membranes and is discharged through the gas outlets in the case. Once a part of the gas outlets is closed as mentioned above, a dischargeability of the gas flowing outside the hollow fiber membranes decreases. Accordingly, a flow rate of the gas in the humidifier and the fuel cell decreases. As a result, the fuel cell system may adversely operate.
Further, if the gas outlets are closed, a pressure loss of the gas flowing outside the hollow fiber membranes is disturbed. Thus, exchange of water cannot be efficiently provided, resulting in an unfavorable humidification.